Chemical sensitizing of photographic emulsions



Patented Apr. 4, 1944 CHEMICAL SENSITIZING F rno'ro- GRAPHIC EMULSIONSArnold Weissberger and Burt H. Carroll, Rochester, N. Y., assignors toEastman Kodak Company, Rochester, N. Y.,

Jersey a corporation of New No Drawing. Application March 21, 1942,

Serial No. 435,666

Claims.

, This invention relates to photographic emulsions and particularly tomaterials used in the preparation of such emulsions.

sensitizing of photographic emulsions is of two general types; chemicalsensitizing, in which the sensitivity of the emulsion is increased inthe spectral region to which the silver halide is originally sensitive,and optical sensitizing, in

which the sensitivity is increased in a spectral region to which thesilver halide is not originally sensitive. The present invention relatesto the former type of sensitizing.

In the chemical sensitizing of photographic emulsions many compoundshave been proposed for the purpose of increasing the sensitivity of thesilver halide grains. Compounds such as sulfur bodies have been proposedand in most cases there is thought to be an interaction of the silverhalide and the sensitizer to form small specks of silver sulfide on thesilver halide grains. These specks are thought to act as nuclei forsilver deposition and thereby to increase the sensitivity of theemulsion.

It is an object of the present invention to provide photographicemulsions having new or improved properties because of the use orpresence therein of materials, the sensitizing properties of which wehave discovered. A further object is to provide a method in which suchmaterials are used to improve photographic emulsions, especiallydeveloping out emulsions, with respect to light sensitivity, by whichterm we include their ability to give the earliest visible impression orimage with the minimum exposure or their ability to produce the maximumdensity after a given exposure or both. A still further object is toprovide colloid products such as gelatins, the usefulness of which forforming light-sensitive photographic emulsions is'greatly increased andcontrolled by the use of our sensitizing materials. A still furtherobject is to provide a method for enhancing the light sensitivity ofphotographic emulsions immediately after the addition of the sensitizingcompounds. Other objects are to increase the general light sensitivityof such photographic emulsions throughout the spectral ranges to whichthey are normally sensitive and to obtain more stable emulsions throughthe use of our sensitizingagents. Other objects will appear from thefollowing description of our invention.

These objects are accomplished according to the present invention byincorporating in a silver halide photographic emulsion anon-sulfurcontaining sensitizing body consisting of analkoxymethylene-fi-diketone.

Our sensitizing material may be used in many Ways. It may beincorporated in emulsions or in colloids used in the preparation of theemulsions. It can also enter the emulsion mixed with other ingredients,organic or inorganic. It increases the light-sensitivity of variousemulsions having different speeds or other distinctive characteristics.While it may be added at different stages of emulsion manufacture,nevertheless it can be very conveniently mixed with the emulsion whenthe latter is otherwise complete and ready for coating. Since its actionis immediate when incorporated, the coating need be delayed only longenough to mix the sensitizing material with it.

The alkoxymethylene-fi-diketones which we have found suitable for thepurpose of sensitizing and stabilizing photographic emulsions includeethoxymethyleneacetyl acetone and butoxymethyleneacetyl acetone as wella other compounds of this general class.

As will be clear to those skilled in the art, the proportion ofsensitizing material added to the emulsions will vary according to theconcentrations of the sensitizing material and according to the increasein light sensitivity desired. We have found that the addition of thealkoxymethylene-c-diketones to photographic emulsions in amounts to theorder of 10 mg. to 50 mg. Per liter of emulsion tends to increase thethreshold speed by .as much as in some cases. Larger amounts ofsensitizing agent can be used and smaller amounts can also be used ifonly slight increase in sensitivity is desired.

Where different batches of emulsion fall below a required manufacturingstandard of light sensitivity, although they may otherwise besatisfactory, sensitivity canreadily be brought up to standard by mixingour sensitizing material with them, the proportion varying with theincrease necessary to produce a uniform product. The increase insensitivity can be effected in one step by thoroughly stirring all ofthe sensitizing material into the emulsion at one time or it may beincorporated in successive steps.

It is convenient to add our sensitizing mate- 25 milligrams of oursensitizing material for each liter of emulsion.

With its light sensitivity increased by the use of our material, theemulsion is melted to the desired degree and is coated on the support,such as suitably subbed glass, film or paper, in the usual way.

The different types of gelatin used for photographic emulsion making maybe used in the example above, hard ones being very useful. Thetemperatures given are, of course, readjusted if the particular gelatinemployed has melting and setting point which deviate considerably fromthe usual ones, this adjustment being a matter of routine control. Oursensitizers can be used to increase the general light-sensitivity ofordinary blue-sensitive photographic emulsions or they can be used forincreasing the sensitivity of orthochromatic, panchromatic, X-ray andother pecial emulsions. It is evident, therefore, that they can be usedin conjunction with optical sensitizers although they do not act asoptical sensitizers for the emulsion. Our sensitizers act to increasethe light sensitivity independently of ripening.

In place of gelatin, ot er colloids may be used in the preparation ofthe photographic emulsion such as collodion, agar, synthetic resins andcellulose esters. Moreover, the principle of the invention is applicableto silver chloride and chlorobromide emulsions as well as to silverbromide and silver bromoiodide emulsions and to mixtures of any two ormore of them.

It will be understood that their invention is to be taken as limitedonly by the scope of the appended claims.

We claim:

1. A photographic emulsion comprising a colloidal material havingparticles of silver halide dispersed therein, and an added sensitizingcompound upon which at least a part of the light sensitivity of theemulsion depends, the sensitizing compound being an alkoxymethylene-fi-diketone.

2. A photographic developing-out gelatino-si'lver halide emulsion ofhigh light sensitivity containing as a sensitizing compound from about10 milligrams to about 50 milligrams per liter of emulsion of an alkoxymethylene acetyl acetone.

3. A photographic developing-out gelatino-silver halide emulsion of highlight sensitivity containing as a seinsitizing compound from about 10milligrams to about 50 milligrams per liter of emulsion ofethoxymethylene acetyl acetone.

4. A photographic developing-out gelatino-silver halide emulsion of highlight sensitivity containing as a sensitizing compound from about 10milligrams to about 50 milligrams per liter of emulsion ofbutoxymethylene acetyl acetone.

5. The process of preparing a gelatino-silver halide emulsion ofincreased light sensitivity which comprises incorporating in saidemulsion an alkoxymethylene fl diketone in sensitizing amount whicheffects an immediate increase in sensitivity.

6. In the process of preparing a developingout gelatino-silver halideemulsion, the method of increasing the light sensitivity of saidemulsion by incorporating in it a sensitizing amount of an alkoxymethylene acetyl acetone.

'7. In the process of preparing a developingoutgelatino-silver halideemulsion, the method of increasing the light sensitivity of saidemulsion by incorporating in it a sensitizing amount of ethoxymethyleneacetyl acetone.

8. In the process of preparing a developingout gelatino-silver halideemulsion, the method of increasing the light sensitivity of saidemulsion by incorporating in it a sensitizing amount of butoxymethyleneacetyl acetone.

9. In the process of preparing a developingout gelatino-silver halideemulsion, the method of increasing the light sensitivity of saidemulsion by incorporating in it from about 10 milligrams to about 50milligrams per liter of emulsion of ethoxymethylene acetyl acetone.

10. In the process of preparing a developingout gelatino-silver halideemulsion, the method of increasing the light-sensitivity which comprisesincorporating therein from about 10 milligrams to about 50 milligramsper liter of emul- 45 sion of butoxymethylene acetyl acetone.

ARNOLD WEISSBERGER. BURT H. CARROLL.

